Zoologger: Necrophiliac spider mite prefers its mate dead

Zoologger is our weekly column highlighting extraordinary animals – and occasionally other organisms – from around the world

Species&colon; The twospotted spider mite (Tetranychus urticae)

Habitat&colon; Native to Europe. It feeds on a wide range of plant hosts, including fruit plants, vegetables and field crops.

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Drop-dead gorgeous. That is how this tiny creature must see its potential mate. The only trouble is, she might have actually dropped dead.

Male twospotted spider mites have a thing for female cadavers killed by a pathogenic fungus. Their mating strategy involves approaching and guarding females that have become immobile during their second larval stage, before they emerge as reproductive adults.

A male is keen to mate with a female as soon as she reaches mating age – so keen, in fact, that he eagerly helps her strip off the exoskeleton that she sheds as she transforms into an adult and can move again. Their first time is crucial because only the sperm from the first mating usually fertilises the eggs.

To stay safe throughout the process, however, males should ideally choose to approach females that are free of deadly pathogens. Indeed, to have any real chance of breeding, they should choose mates that are actually alive.

But when a team lead by Nina Trandem of the Norwegian Institute for Agricultural and Environmental Research (Bioforsk) in Ås, Norway, presented male spider mites with healthy immobile females and others that had been killed by the pathogenic fungus Neozygites floridana, they were in for a shock.

This is feasible, says Kelly Weinersmith of Rice University in Houston, Texas, but she adds that follow-up studies are needed to confirm it.

“There is definitely evidence of parasites giving out scents to try to attract the next host,” she says. An example of this is a malaria parasite that produces a lemony scent to draw mosquitoes to infected hosts.

But necrophiliac animals typically don’t benefit from their affinity for cadavers.

“Necrophilia in birds and non-human mammals is not a functional strategy but a mistake,” says Kees Moeliker from the Natural History Museum Rotterdam in the Netherlands, who described a case of homosexual duck necrophilia, in which a drake mallard copulated with a dead male for 75 minutes. They tend to be unaware that their object of attraction is in fact dead, he says.